This invention relates generally to the field of micro-electrical-mechanical systems (MEMS), and in particular, to improved MEMS devices and methods of making same for use with fiber-optic communications systems.
The Internet and data communications are causing an explosion in the global demand for bandwidth. Fiber optic telecommunications systems are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM) to expand the capacity of new and existing optical fiber systems to help satisfy this demand. In DWDM, multiple wavelengths of light simultaneously transport information through a single optical fiber. Each wavelength operates as an individual channel carrying a stream of data. The carrying capacity of a fiber is multiplied by the number of DWDM channels used. Today DWDM systems employing up to 80 channels are available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual channels (or circuits) to individual destination points, such as an end customer or to another network. Systems that perform these functions are called cross-connects. Additionally, there is the need to add or drop particular channels at an intermediate point. Systems that perform these functions are called add-drop multiplexers (ADMs). All of these networking functions are currently performed by electronicsxe2x80x94typically an electronic SONET/SDH system. However SONET/SDH systems are designed to process only a single optical channel. Multi-wavelength systems would require multiple SONET/SDH systems operating in parallel to process the many optical channels. This makes it difficult and expensive to scale DWDM networks using SONET/SDH technology.
The alternative is an all-optical network. Optical networks designed to operate at the wavelength level are commonly called xe2x80x9cwavelength routing networksxe2x80x9d or xe2x80x9coptical transport networksxe2x80x9d (OTN). In a wavelength routing network, the individual wavelengths in a DWDM fiber must be manageable. New types of photonic network elements operating at the wavelength level are required to perform the cross-connect, ADM and other network switching functions. Two of the primary functions are optical add-drop multiplexers (OADM) and wavelength-selective cross-connects (WSXC).
In order to perform wavelength routing functions optically today, the light stream must first be de-multiplexed or filtered into its many individual wavelengths, each on an individual optical fiber. Then each individual wavelength must be directed toward its target fiber using a large array of optical switches commonly called an optical cross-connect (OXC). Finally, all of the wavelengths must be re-multiplexed before continuing on through the destination fiber. This compound process is complex, very expensive, decreases system reliability and complicates system management. The OXC in particular is a technical challenge. A typical 40-80 channel DWDM system will require thousands of switches to fully cross-connect all the wavelengths. Opto-mechanical switches, which offer acceptable optical specifications are too big, expensive and unreliable for widespread deployment. Improvements are needed to help reliably switch and direct the various wavelengths along their desired paths.
Micro-electrical-mechanical systems (MEMS) theoretically provide small systems capable of providing switching functions. However, MEMS also have difficulties to overcome. For example, voltages needed to rotate the micromirror often are larger than desired, resulting in distortion of the mirror shape. The present invention is, therefore, directed to improved MEMS devices for use with a wide range of OTN equipment, including switches (OXC) and routers.
The present invention provides improved MEMS devices for use with all optical networks, and methods of using and making same. For example, the present invention may be used with the exemplary wavelength routers described in co-pending U.S. patent application Ser. No. 09/442,061, filed Nov. 16, 1999, which application will issue on Dec. 31, 2002 as U.S. Pat. No. 6,501,877, the complete disclosure of which is incorporated herein by reference.
In one embodiment, a structure for steering light is provided. The structure includes a base layer, a first conductive layer overlying a portion of the base layer, and a flexure assembly overlying a portion of the first conductive layer. A portion of the flexure assembly has an I-beam configuration. The beam layer overlies and is coupled to the flexure assembly, and is adapted to rotate relative to the base layer.
In one aspect, a second conductive layer overlies a portion of the first conductive layer, with the first conductive layer having a greater surface area than the second conductive layer. In another similar aspect, the device includes a third conductive layer overlying a portion of the second conductive layer, with the second conductive layer having a greater surface area than the third conductive layer
In one embodiment, a portion of underlying edges of the flexure assembly and beam layer are adapted to contact the base layer upon rotation of the beam layer. In this manner, the beam layer is rotated by an underlying rotation device. Further, the multi-point contact between the underlying edges and the base layer provides a stable platform for the beam layer.
In some embodiments, the base layer includes a non-conductive material, the beam layer comprises an electrically conductive material, and/or the conductive layer(s) include polysilicon. In one aspect, the beam layer is electrically isolated from the conductive layers.
In one aspect, the flexure assembly includes a torsion beam having first and second generally parallel arms each coupled to a central beam that is generally orthogonal to the arms. In another aspect, the arms also are coupled to the beam layer to provide support thereto.
In one aspect, the first and second conductive layers each have a central portion separate from remaining portions of the respective conductive layers. The central portions are coupled together. In another aspect, the flexure assembly includes a central portion that is coupled to the second conductive layer central portion. In this manner, the central portions help facilitate rotation of the flexure assembly, and help electrically isolate the beam layer from the remaining portions of the first and second conductive layers.
In one aspect, the first, second and third conductive layers are in separate planes. In another aspect, the first, second and third conductive layers have at least portions thereof electrically coupled together, with the electrically coupled portions adapted to operate together as a single electrode.
In one particular aspect, the underlying edges of the flexure assembly and beam layer are configured to simultaneously contact the base layer upon rotation of the beam layer. In this manner, the underlying edges of two or more layers provide a stable multi-point landing system for the beam layer. Further, the beam layer preferably has a substantially planar upper surface when the underlying edges are in contact with the base layer.
In one embodiment, an apparatus for steering light according to the present invention includes a base layer, a first conductive layer overlying the base layer, and a second conductive layer. Each of the first and second conductive layers are in a separate plane from the other, and each conductive layer includes at least a portion thereof that is electrically coupled to at least a portion of the other conductive layer. A beam layer is coupled to a rotation device, with the rotation device positioned between at least one of the conductive layers and the beam layer. The rotation device and beam layer rotate in response to a voltage applied to the coupled portions of the conductive layers. In this manner, the conductive layers together are used to rotate the beam layer. Due at least in part to the positioning of the conductive layers, a lower threshold voltage is used to rotate the beam layer as compared to using a single conductive layer.
In one aspect, the present invention further includes a third conductive layer, with each of said first, second and third conductive layers in a separate plane from the other two conductive layers, and each having at least a portion thereof that is electrically coupled to at least a portion of the other two conductive layers.
In one aspect, an underlying edge of the beam layer is adapted to contact the base layer at a first location when a first voltage is applied to the electrically coupled conductive layer portions, and to contact the base layer at a second location when a second voltage is applied. In another aspect, the rotation device includes a torsion beam underlying the beam layer and having at least a portion thereof comprising an I-beam.
The present invention further provides exemplary methods for making an apparatus for steering light. In one embodiment, the method includes providing a base layer having first and second portions. First and second stacked electrodes are formed on the first and second portions, with the stacked electrodes on the first portion electrically isolated from the stacked electrodes on the second portion. A flexure assembly is formed coupled to the base layer and electrically isolated from the first and second stacked electrodes. A beam layer is coupled to the flexure assembly. The flexure assembly and stacked electrodes may have some or all of the characteristics described above.
In one aspect, the method further includes formed a third stacked electrode overlying the second stacked electrode. In one embodiment, each subsequently formed electrode has about the same surface area, or a smaller surface area, than the immediately underlying electrode.
The present invention further provides methods for steering light. In one embodiment, a structure for steering light as previously described is provided. A voltage is applied to the first and second conductive layers to rotate the beam layer to a desired position. The beam layer has a substantially planar upper surface when in the desired position. The method includes directing a light at the beam layer.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.